The invention relates to a process for removing contaminants from used oil by subjecting the oil to vaporization and pyrolysis, whereby coke is formed. The contaminants remain with the coke, which can be separated from the oil. The invention further relates to a rotating, indirectly heated retort or reactor in which the process is practised.
Processes are known for reclaiming oil from contaminated used oil (sometimes referred to as waste oil).
One such process is disclosed in U.S. Pat. No. 5,271,808, issued Dec. 21, 1993 to Shurtleff. Shurtleff discloses a process wherein an inclined boiler heats the waste oil, vaporizing and driving off lighter hydrocarbons at temperatures of about 650xc2x0 F. Heavier hydrocarbons and contaminants, amounting to about 10% of the original oil, collect as a sludge in the bottom of the boiler. The sludge drains for disposal. The lighter hydrocarbons are condensed as a reclaimed oil product.
However, Shurtleff""s process produces an oily waste which itself requires specialized disposal.
Other methods which can produce a reclaimed oil and an oil-dry contaminant typically involve subjecting the waste oil to thermal pyrolysis.
For example, in U.S. Pat. No. 5,423,891, issued to Taylor, a process is disclosed for the gasification of solids waste. Heat carrier solids (HCS) are first heated and then fed co-currently with hydrocarbon-bearing solids waste through a rotary kiln retort. The solids waste and HCS co-mingle, transferring heat. The resulting temperatures of 1200 to 1500xc2x0 F. are suitable to thermally pyrolyse the hydrocarbons in the waste. The resultant vapours are extracted for condensation. The retort solids and HCS are discharged from the kiln for recovery of the retort solids and re-heating of the HCS.
In Taylor""s system the HCS are continuously circulated in a material handling loop. The HCS is a coarse granular solid which is heated outside the kiln and gives up its heat inside the kiln. Transport of the HCS around the loop involves considerable materials-handling equipment.
In U.S. Pat. No. 4,473,464, issued to Boyer et al., a process is disclosed for treating heavy crude oil. Carbonaceous solids are finely ground for concurrent feed with crude oil to an indirectly heated kiln. Pyrolysed hydrocarbon vapours are condensed. Coke and carbonaceous solids are screened, ground and recycled outside the kiln. Heat loss to the solids is minimized and the crude oil is preheated to a temperature high enough to balance any temperature loss by the solids.
U.S. Pat. No. 4,303,477, issued to Schmidt et al., discloses co-currently adding a consumable fine-grained reactive solid to a waste material for binding metal and sulfur contaminants during treatment. The reactive solids, such as lime having a grain size typically less than 1 mm, and waste are thermally cracked as they progress through a rotating, indirectly fired kiln. The solids make a single pass through the kiln, the reactive solid being consumed in the process.
Some of the above described prior art processes involve significant material handling challenges in the recycling and conveyancing of large masses of hot, coarse solids. Other processes, which do not recycle hot solids, involve rejection of a portion of the oily waste or irreversibly consume a catalyst.
There is therefore a need for a simplified process for separating contaminants from used oils. It is the objective of the present invention to provide such a process.
The present invention provides a simple apparatus and process for reclaiming oil from used, contaminated oil feed. In general, the process comprises feeding used oil through a feed line to a rotating thermal reactor wherein the oil is pyrolysed to produce hydrocarbon vapour and coke. The contaminants become associated with the coke. The vapour and coked solids are removed from the reactor. The vapour is condensed to produce a contaminant-free oil product and the contaminant-rich coked solids are collected for disposal, possibly as feed for a cement kiln.
The equipment used includes a reactor comprising a rotating vessel housed in a heating chamber, means for feeding used oil into the rotating vessel, and an oil recovery system comprising a vapour extraction pipe, a solids removal cyclone, and vapour condensation equipment.
More particularly, the rotating vessel is indirectly heated so that its internal surfaces are sufficiently hot to vaporize and pyrolyse the feed oil. The feed oil is introduced into the vessel chamber wherein it vaporizes and pyrolyses, forming hydrocarbon vapour and coke. Metals and other contaminants become associated with the coke. A charge of coarse granular solids is provided within the vessel chamber. As the vessel rotates, the granular solids scour the vessel""s internal surface and comminute the coke into fine solids. The fine solids may include solids introduced with the feed oil. The vapour is extracted from the vessel chamber through an axial pipe. The fine solids are separated within the vessel chamber from the coarse granular solids for removal from the vessel, preferably using a spiral chute. The chute spirals from a screened entrance at the vessel""s circumference to a discharge outlet at the vessel""s axis. The chute""s screen excludes coarse solids and collects only the fine solids. The fine solids are conveyed out of the vessel for disposal. Fine solids may also be elutriated with the vapours. Any fine solids associated with the vapours are separated out. The substantially solids-free vapours are then condensed to yield product oil. The contaminant-rich fine solids are collected for disposal.
Only a small portion of the feed oil is converted to coke, the remainder being recovered as a substantially contaminant-free product oil.
In one embodiment, the invention is concerned with a thermal process for removing water, metal and halide contaminants from used oil comprising: providing a rotating vessel having a circumferential wall and end walls forming an internal reaction zone; providing a charge of non-ablating coarse granular solids which form a bed within the reaction zone; heating the outside of the vessel so as to indirectly heat the reaction zone and the bed of coarse granular solids by conduction through the vessel""s walls; feeding contaminated used oil through one of the vessel""s end walls so that it discharges into the reaction zone; vaporizing and pyrolyzing the oil within the heated reaction zone to produce hydrocarbon vapours and deposit coke, whereby contaminants become associated with the coke; scouring the vessel walls with the bed of coarse granular solids to remove coke deposits and comminute coke into fine solids; removing the hydrocarbon vapours and fine solids from the reaction zone; separating the fine solids and hydrocarbon vapours; and condensing the hydrocarbon vapours to recover substantially contaminant-free product oil.